SweetFX "shared" shaders appear to be free?

I notice we can add extra SweetFX "shared" shaders at virtually no extra GPU expense. I presume this is because the code of the "shared" shaders is grouped together into a single pass inside Shared.h? But then that leaves me wondering why it couldn't be done this way for all shaders? Or is this one of the things ReShade 3.0 solves? (apologies as I don't have time to read through all the release notes / changelog ).